Ultraviolet (UV) lamp systems are commonly used for heating and curing materials such as adhesives, sealants, inks, and coatings. Certain ultraviolet lamp systems have electrodeless light sources and operate by exciting an electrodeless plasma lamp with microwave energy. In an electrodeless ultraviolet lamp system that relies upon excitation with microwave energy, the electrodeless lamp is mounted within a metallic microwave cavity or chamber. One or more microwave generators, such as magnetrons, are coupled via waveguides with the interior of the microwave chamber. The magnetrons supply microwave energy to initiate and sustain a plasma from a gas mixture enclosed in the electrodeless lamp. The plasma emits a characteristic spectrum of electromagnetic radiation strongly weighted with spectral lines or photons having ultraviolet and infrared wavelengths.
To irradiate a substrate, the ultraviolet light is directed from the microwave chamber through a chamber outlet to an external location. The chamber outlet is capable of blocking emission of microwave energy while allowing ultraviolet light to be transmitted outside the microwave chamber. A fine-meshed metal screen covers the chamber outlet of many conventional ultraviolet lamp systems. The openings in the metal screen transmit the ultraviolet light for irradiating a substrate positioned outside the microwave chamber; yet substantially block the emission of microwave energy.
In order to protect operators of the ultraviolet lamp systems, RF sensing devices are placed between the operator and the lamp. These RF sensing devices are connected to microwave energy detectors, which are set, based on OSHA standards (similar to standards for microwave ovens), to detect microwave energy in excess of a predetermined amount, e.g., about 5 mW/cm2. If microwave energy output levels exceed this amount, the microwave energy detector is configured to shut down the system to limit the exposure of the operator to the microwave energy.
Microwave energy detectors may contain some components that are radiation sensitive. The microwave energy detectors can become damaged and not accurately report excessive microwave energy emissions if one or more of the radiation sensitive components fails. For example, the mesh screens that are used to cover the chamber outlets and block microwave energy are typically made of metals such as tungsten wire and are fairly delicate so they may be easily damaged, allowing microwave energy out of the microwave cavity. In extreme cases, attempts to operate the ultraviolet lamp system may be made with the protective screen removed. In these cases the detector should prevent the operation of the lamp system. However, the detector and supporting circuitry may be damaged by the excess microwave energy and damaged in such a way that the detector allows continued operation of the lamp system as damaged components become open or short circuits.